This invention relates to open cycle vapor compression heat pumps and, more particularly, to a system and a process employing open cycle vapor compression heat pumps in a parallel arrangement to transfer heat.
Conventional heat pumps provide either heat or refrigeration by employing a vapor compression cycle to transfer heat between a heat source and a heat sink. In operation, a simple cycle heat pump adds sufficient heat by compression to a working fluid vapor to raise the heat content of the vapor from the level of the heat source to that of the heat sink. The efficiency of such a cycle is given in terms of its Coefficient Of Performance (COP), which is approximately proportional to T.sub.H /(T.sub.H -T.sub.L) where T.sub.H and T.sub.L are the absolute temperatures of the heat sink and of the heat source respectively.
Heat pump efficiency can be increased through the modification of this simple vapor compression cycle to include multi-stage compression as described in "Applications of Thermodynamics" by Bernard D. Wood (Addison-Wesley Publishing Company, 1969) pages 186-188. In this configuration the heat of compression is imparted into working fluid vapor through a progression of series-connected compressive stages. However, as in the simple cycle, the multi-stage heat pump requires that sufficient heat of compression be added to raise the heat content of the entire working fluid vapor flow from the heat level of the heat source to that of the heat sink.
Greater efficiency can be achieved in a heat pump system wherein a plurality of heat pumps are arranged in parallel intermediate a heat sink and a heat source, with each heat pump having a predeterminedly different thermal transfer capacity. Thusly, each of the working fluid flows is imparted with a distinctly different amount of heat energy corresponding to the capacity of its respective heat pump.
In such a parallel-arranged system only one heat pump operates between the entire heat source/heat sink temperature range, and thus has a COP proportional to that of the simple single-flow heat pump system (re: COP.alpha.T.sub.H /T.sub.H -T.sub.L). The remaining heat pumps operate between a reduced temperature range, and thus have higher COP's than that associated with the simple cycle system, thereby making the combined COP of the parallel-arranged system greater than for a comparable simple single-flow system. For example, in a parallel-arranged heat pump system operating in a cooling mode between T.sub.H and T.sub.L, a first heat pump might operate between T.sub.L and T.sub.1, with T.sub.1 &lt;T.sub.H. Therefore COP.sub.1 =T.sub.1 /(T.sub.1 -T.sub.L)&gt;T.sub.H /(T.sub.H -T.sub.L).
The Templifier.RTM. industrial heat pump system commercially available from the Westinghouse Corporation apparently utilizes a concept somewhat related to that of a parallel-arranged heat pump system. However, the Templifier.RTM. system employs closed cycle heat pumps, and does not therefore enjoy the benefits associated with open cycle heat pumps. In particular, open cycle heat pumps do not require heat exchangers as do closed cycle designs, thereby resulting in capital cost and space savings and in the beneficial elimination of inefficient temperature drops attendant the use of heat exchangers. Moreover, the seals often required to isolate different liquid-based flows in closed cycle heat pumps are not required in open cycle designs.
An example of an open cycle heat pump is contained in the Article "Geothermal Powered Heat Pumps to Produce Process Heat" by D. T. Neill and W. P. Jensen (11th Report of the Intersociety Energy Conservation and Engineering Conference, September, 1976). However, the Neill, et al system does not include parallel arranged heat pumps and thus does not obtain the benefits derivable therefrom.
Accordingly, an object of the present invention is to provide a new and improved heat pump system.
Another object of the present invention is to provide a heat pump system with an improved coefficient of performance.
Another object of the present invention is to provide a new and improved heat pump system with the advantages attendant an open cycle system.
Still another object of the present invention is to provide a process for transferring heat from a heat source to a heat sink which eliminates the inefficiencies of a closed cycle device and which exhibits an improved coefficient of performance.